[gta02-core] Audio ECNs, a bit of progress

[Rene Harder]

Werner Almesberger wrote:
> Some news from the ECN front:
>
> - I finished ECN0031, which describes how to use the codec interrupt
>   for HOLD and JACK_INSERT instead of involving the CPU directly.
>   This is from Joerg's "Mega-ECN".
>   

So far, looks good to me, I'll do a full review later today.

> - I updated ECN0015 (removal of the Calypso's rear entrance through
>   the audio jack) with the changes that have actually been done.
>
>   I wonder if we shouldn't get rid of R4405/7 completely instead of
>   making them 0R. We'll have to add some EMI and ESD protection, so
>   there will be room for interrupting the circuit, if necessary.
>   

Thanks, I planed on removing them that's why I wrote this into the ECN.
Actually, I wanted to discuss this first but I probably forgot about it.
Any comments? Otherwise I'll remove them.

>   Once the final fate of R4405/7 is decided, we can move ECN0015
>   to "Done".
>
> - we have one regression: the ESD protectors D3001 and D3002 (at
>   the front speaker) were lost in translation.
>   

Right, they got lost. I'll add them.

> I still have more items to process from the "mega-ECN". Here's my
> "to do" list:
>
> - new ECN: add ESD to jack
>   
Yes, it's probably a really good idea to add ESD protection to all pins
of the Jack as it is in Joerg's  proposal.

> - buzz prevention: remove 22 pF caps around jack, place EMI filters
>   (C4403, C4404, C4405), remove common-mode choke B4102
>   

I'd definitely go for the Pi filter in all of the headphone lines and
remove B4102.

> - bass fix: add component, remove R4405/7 (0R for us)
>
> - bass fix: big caps (~100 uF), tantalum, no cer
>
> - new suppression:
>   we might consider making each of C3012/13 a 4u7 + 47p couple
>   as that should rather completely short any RF induced to the "hot" side of
>   those C (chip side) to GND
>
> - buzz fix: provide place for bigC
>
> - rear ECN: merge 18 pF + 47 pF into 56 pF
>   

Do we have already 56pF in the BOM or does that mean we need a new
component?

> - new ECN: swap rear choke / caps
>
> - new ECN: remove C3020
>   
Sure, it's NC right now, so there shouldn't be a problem with removing
C3020.

> - new ECN: increase input caps from 100 nF to 1 uF (ceramic)
>   (1uF) according to wolfson appnotes
>   - mic out caps
>   - RXN/RXP (modem to codec)
>   - MONO1/MONO2 (codec to modem)
>
> - new ECN: route LOUT1/ROUT2 back to LINE1/LINE2
>   

This needs to be checked more in detail because we'd use polarized
tantalum caps for output coupling which can get damaged when operated
inverse.


Rene